Method and apparatus for small cell enhancement in a wireless communication system

ABSTRACT

A method and apparatus are disclosed for small cell enhancement in a wireless communication network, wherein a UE (User Equipment) is configured with DRX and is served by a first cell that is configured with a PDCCH (Physical Downlink Control Channel). The method includes the UE receives an RRC (Radio Resource Control) message for configuring a second cell to the UE, wherein the second cell is configured with a PDCCH. The method also includes the UE maintains separate drx-InactivityTimers for the first cell and the second cell.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present Application claims the benefit of U.S. Provisional Patent Application Serial No. 61/699,428 filed on Sep. 11, 2012, the entire disclosure of which is incorporated herein by reference.

FIELD

This disclosure generally relates to wireless communication networks, and more particularly, to a method and apparatus for small cell enhancement in a wireless communication system.

BACKGROUND

With the rapid rise in demand for communication of large amounts of data to and from mobile communication devices, traditional mobile voice communication networks are evolving into networks that communicate with Internet Protocol (IP) data packets. Such IP data packet communication can provide users of mobile communication devices with voice over IP, multimedia, multicast and on-demand communication services.

An exemplary network structure for which standardization is currently taking place is an Evolved Universal Terrestrial Radio Access Network (E-UTRAN). The E-UTRAN system can provide high data throughput in order to realize the above-noted voice over IP and multimedia services. The E-UTRAN system's standardization work is currently being performed by the 3GPP standards organization. Accordingly, changes to the current body of 3GPP standard are currently being submitted and considered to evolve and finalize the 3GPP standard.

SUMMARY

A method and apparatus are disclosed for small cell enhancement in a wireless communication network, wherein a UE (User Equipment) is configured with DRX (Discontinuous Reception) and is served by a first cell that is configured with a PDCCH (Physical Downlink Control Channel). The method includes the UE receives an RRC (Radio Resource Control) message for configuring a second cell to the UE, wherein the second cell is configured with a PDCCH. The method also includes the UE maintains separate drx-InactivityTimers for the first cell and the second cell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagram of a wireless communication system according to one exemplary embodiment.

FIG. 2 is a block diagram of a transmitter system (also known as access network) and a receiver system (also known as user equipment or UE) according to one exemplary embodiment.

FIG. 3 is a functional block diagram of a communication system according to one exemplary embodiment.

FIG. 4 is a functional block diagram of the program code of FIG. 3 according to one exemplary embodiment.

FIG. 5 is a timing diagram according to one exemplary embodiment.

FIG. 6 is a flow chart according to one exemplary embodiment.

FIG. 7 is a flow chart according to one exemplary embodiment.

DETAILED DESCRIPTION

The exemplary wireless communication systems and devices described below employ a wireless communication system, supporting a broadcast service. Wireless communication systems are widely deployed to provide various types of communication such as voice, data, and so on. These systems may be based on code division multiple access (CDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), 3GPP LTE (Long Term Evolution) wireless access, 3GPP LTE-A or LTE-Advanced (Long Term Evolution Advanced), 3GPP2 UMB (Ultra Mobile Broadband), WiMax, or some other modulation techniques.

In particular, the exemplary wireless communication systems devices described below may be designed to support one or more standards such as the standard offered by a consortium named “3rd Generation Partnership Project” referred to herein as 3GPP, including Document Nos. 3GPP TS 36.321 V10.5.0, “E-UTRA MAC protocol specification (Release 10)”; 3GPP TS 36.331 V10.5.0, “E-UTRA RRC protocol specification (Release 10)”; RWS-120052, “Summary of TSG-RAN Workshop on Release 12 and Onwards”; RWS-120003, “LTE Release 12 and Beyond”; RWS-120010, “Requirements, Candidate Solutions & Technology Roadmap for LTE Rel-12 Onward”; and RWS-120046, “Technologies for Rel-12 and Onwards”. The standards and documents listed above are hereby expressly incorporated herein.

FIG. 1 shows a multiple access wireless communication system according to one embodiment of the invention. An access network 100 (AN) includes multiple antenna groups, one including 104 and 106, another including 108 and 110, and an additional including 112 and 114. In FIG. 1, only two antennas are shown, for each antenna group, however, more or fewer antennas may be utilized for each antenna group. Access terminal 116 (AT) is in communication with antennas 112 and 114, where antennas 112 and 114 transmit information to access terminal 116 over forward link 120 and receive information from access terminal 116 over reverse link 118. Access terminal (AT) 122 is in communication with antennas 106 and 108, where antennas 106 and 108 transmit information to access terminal (AT) 122 over forward link 126 and receive information from access terminal (AT) 122 over reverse link 124. In a FDD system, communication links 118, 120, 124 and 126 may use different frequency for communication. For example, forward link 120 may use a different frequency then that used by reverse link 118.

Each group of antennas and/or the area in which they are designed to communicate is often referred to as a sector of the access network. In the embodiment, antenna groups each are designed to communicate to access terminals in a sector of the areas covered by access network 100.

In communication over forward links 120 and 126, the transmitting antennas of access network 100 may utilize beamforming in order to improve the signal-to-noise ratio of forward links for the different access terminals 116 and 122. Also, an access network using beamforming to transmit to access terminals scattered randomly through its coverage causes less interference to access terminals in neighboring cells than an access network transmitting through a single antenna to all its access terminals.

An access network (AN) may be a fixed station or base station used for communicating with the terminals and may also be referred to as an access point, a Node B, a base station, an enhanced base station, an eNodeB, or some other terminology. An access terminal (AT) may also be called user equipment (UE), a wireless communication device, terminal, access terminal or some other terminology.

FIG. 2 is a simplified block diagram of an embodiment of a transmitter system 210 (also known as the access network) and a receiver system 250 (also known as access terminal (AT) or user equipment (UE)) in a MIMO system 200. At the transmitter system 210, traffic data for a number of data streams is provided from a data source 212 to a transmit (TX) data processor 214.

In one embodiment, each data stream is transmitted over a respective transmit antenna. TX data processor 214 formats, codes, and interleaves the traffic data for each data stream based on a particular coding scheme selected for that data stream to provide coded data.

The coded data for each data stream may be multiplexed with pilot data using OFDM techniques. The pilot data is typically a known data pattern that is processed in a known manner and may be used at the receiver system to estimate the channel response. The multiplexed pilot and coded data for each data stream is then modulated (i.e., symbol mapped) based on a particular modulation scheme (e.g., BPSK, QPSK, M-PSK, or M-QAM) selected for that data stream to provide modulation symbols. The data rate, coding, and modulation for each data stream may be determined by instructions performed by processor 230.

The modulation symbols for all data streams are then provided to a TX MIMO processor 220, which may further process the modulation symbols (e.g., for OFDM). TX MIMO processor 220 then provides N_(T) modulation symbol streams to N_(T) transmitters (TMTR) 222 a through 222 t. In certain embodiments, TX MIMO processor 220 applies beamforming weights to the symbols of the data streams and to the antenna from which the symbol is being transmitted.

Each transmitter 222 receives and processes a respective symbol stream to provide one or more analog signals, and further conditions (e.g., amplifies, filters, and upconverts) the analog signals to provide a modulated signal suitable for transmission over the MIMO channel. N_(T) modulated signals from transmitters 222 a through 222 t are then transmitted from N_(T) antennas 224 a through 224 t, respectively.

At receiver system 250, the transmitted modulated signals are received by N_(R) antennas 252 a through 252 r and the received signal from each antenna 252 is provided to a respective receiver (RCVR) 254 a through 254 r. Each receiver 254 conditions (e.g., filters, amplifies, and downconverts) a respective received signal, digitizes the conditioned signal to provide samples, and further processes the samples to provide a corresponding “received” symbol stream.

An RX data processor 260 then receives and processes the N_(R) received symbol streams from N_(R) receivers 254 based on a particular receiver processing technique to provide N_(T) “detected” symbol streams. The RX data processor 260 then demodulates, deinterleaves, and decodes each detected symbol stream to recover the traffic data for the data stream. The processing by RX data processor 260 is complementary to that performed by TX MIMO processor 220 and TX data processor 214 at transmitter system 210.

A processor 270 periodically determines which pre-coding matrix to use (discussed below). Processor 270 formulates a reverse link message comprising a matrix index portion and a rank value portion.

The reverse link message may comprise various types of information regarding the communication link and/or the received data stream. The reverse link message is then processed by a TX data processor 238, which also receives traffic data for a number of data streams from a data source 236, modulated by a modulator 280, conditioned by transmitters 254 a through 254 r, and transmitted back to transmitter system 210.

At transmitter system 210, the modulated signals from receiver system 250 are received by antennas 224, conditioned by receivers 222, demodulated by a demodulator 240, and processed by a RX data processor 242 to extract the reserve link message transmitted by the receiver system 250. Processor 230 then determines which pre-coding matrix to use for determining the beamforming weights then processes the extracted message.

Turning to FIG. 3, this figure shows an alternative simplified functional block diagram of a communication device according to one embodiment of the invention. As shown in FIG. 3, the communication device 300 in a wireless communication system can be utilized for realizing the UEs (or ATs) 116 and 122 in FIG. 1, and the wireless communications system is preferably the LTE system. The communication device 300 may include an input device 302, an output device 304, a control circuit 306, a central processing unit (CPU) 308, a memory 310, a program code 312, and a transceiver 314. The control circuit 306 executes the program code 312 in the memory 310 through the CPU 308, thereby controlling an operation of the communications device 300. The communications device 300 can receive signals input by a user through the input device 302, such as a keyboard or keypad, and can output images and sounds through the output device 304, such as a monitor or speakers. The transceiver 314 is used to receive and transmit wireless signals, delivering received signals to the control circuit 306, and outputting signals generated by the control circuit 306 wirelessly.

FIG. 4 is a simplified block diagram of the program code 312 shown in FIG. 3 in accordance with one embodiment of the invention. In this embodiment, the program code 312 includes an application layer 400, a Layer 3 portion 402, and a Layer 2 portion 404, and is coupled to a Layer 1 portion 406. The Layer 3 portion 402 generally performs radio resource control. The Layer 2 portion 404 generally performs link control. The Layer 1 portion 406 generally performs physical connections.

In general, carrier aggregation (CA) is a feature to support wider bandwidth in LTE-Advanced (LTE-A). A terminal may simultaneously receive or transmit on one or multiple component carriers depending on its capabilities.

In addition to a primary serving cell (PCell), a UE in RRC_CONNECTED mode may be configured with other secondary serving cells (SCell). The PCell is considered as always activated, while an Activation/Deactivation MAC control Element (CE) could be used to activate or deactivate an Scell (as discussed in 3GPP TS 36.321 V10.5.0). An sCellDeactivationTimer corresponding to the SCell may also be used for SCell status maintenance—i.e., when the sCellDeactivationTimer expires, the corresponding SCell would be implicitly considered as deactivated. A configured SCell may contain downlink (DL) resources only (such as a DL CC) or DL resources as well as uplink (UL) resources (such as a DL CC and an UL CC), as discussed in 3GPP TS 36.331 V10.5.0.

As discussed in 3GPP TS 36.321 V10.5.0, A discontinuous reception (DRX) functionality is specified in the 3GPP MAC specification as follows:

5.7 Discontinuous Reception (DRX)

The UE may be configured by RRC with a DRX functionality that controls the UE's PDCCH monitoring activity for the UE's C-RNTI, TPC-PUCCH-RNTI, TPC-PUSCH-RNTI and Semi-Persistent Scheduling C-RNTI (if configured). When in RRC_CONNECTED, if DRX is configured, the UE is allowed to monitor the PDCCH discontinuously using the DRX operation specified in this subclause; otherwise the UE monitors the PDCCH continuously. When using DRX operation, the UE shall also monitor PDCCH according to requirements found in other subclauses of this specification. RRC controls DRX operation by configuring the timers onDurationTimer, drx-InactivityTimer, drx-Retransmission Timer (one per DL HARQ process except for the broadcast process), the longDRX-Cycle, the value of the drxStartOffset and optionally the drxShortCycleTimer and shortDRX-Cycle. A HARQ RTT timer per DL HARQ process (except for the broadcast process) is also defined (see subclause 7.7). When a DRX cycle is configured, the Active Time includes the time while:

-   -   onDurationTimer or drx-InactivityTimer or         drx-RetransmissionTimer or mac-ContentionResolutionTimer (as         described in subclause 5.1.5) is running; or     -   a Scheduling Request is sent on PDCCH and is pending (as         described in subclause 5.4.4); or     -   an uplink grant for a pending HARQ retransmission can occur and         there is data in the corresponding HARQ buffer; or     -   a PDCCH indicating a new transmission addressed to the C-RNTI of         the UE has not been received after successful reception of a         Random Access Response for the preamble not selected by the UE         (as described in subclause 5.1.4).         When DRX is configured, the UE shall for each subframe:     -   during the Active Time, for a PDCCH-subframe, if the subframe is         not required for uplink transmission for half-duplex FDD UE         operation and if the subframe is not part of a configured         measurement gap:         -   monitor the PDCCH;         -   if the PDCCH indicates a new transmission (DL or UL):             -   start or restart drx-InactivityTimer.

Furthermore, RWS-120052 summarizes the TSG-RAN workshop on release 12 and onwards, and lists several requirements and potential technologies for Rel-12 and onwards. To increase the network capacity for coping with traffic explosion, small cell enhancement is proposed.

In general, higher network capacity can be achieved by the deployments of complementary low-power nodes (with small cells) under the coverage of an existing macro-node layer (with macro cells), as discussed in RWS-120003. In such a heterogeneous deployment, the low-power nodes would provide very high traffic capacity and service level (end-user throughput) locally (e.g., in indoor and hot-spot outdoor positions), while the macro layer provides full-area coverage. Thus, the layer with low-power nodes could also be referred to as providing local-area access, in contrast to the wide-area-covering macro layer.

In RWS-120010, it has been proposed to split C-plane signalling and U-plane data between macro cell and small cell, such that C-plane signalling would go through macro cell for good connectivity and mobility and U-plane data would go through small cell for higher throughput and more cost-energy efficient operations. There could be no conventional cell-specific signals/channels (e.g., PSS/SSS, CRS, MIB/SIB in a small cell) so that more resources could be used for traffic.

In Rel-10/11 CA, only intra-eNB CA is allowed. In other words, only CCs under the same eNB could be aggregated. Inter-eNB CA is proposed in RWS-120046. For example, the macro cells are controlled by serving eNBs (SeNBs) and the small cells are controlled by Drift eNBs (DeNB). Accordingly, a new interface between SeNB and DeNB is required. And, some enhancements on RAN1/2 need to be considered, such as D-eNB UL control information handling and RACH Msg2 (i.e., random access response) from D-eNB. To remove the requirement for a low-latency interconnection between SeNB and DeNB, it has been further proposed in RWS-120003 to have separate schedulers in SeNB and DeNB, which implies there will be separate PDCCHs (Physical Downlink Control Channel) on the macro cell and the small cell for scheduling resources for UE uplink transmissions.

In Rel-10/11 CA, there is only one drx-InactivityTimer, and a UE has to monitor PDCCHs on all scheduling cells if this timer is running. This timer should be restarted each time when the UE receives a PDCCH indicating a new transmission.

When small cells are deployed in a heterogeneous network for increasing capacity, the traffic for most of the time will go through the small cell. According to the current DRX functionality, the UE needs to monitor the macro cell if the drx-InactivityTimer is running, even if there is little chance of traffic via the macro cell. As shown the timing diagram 500 in FIG. 5, the drx-InactivityTimer is extended (from start time T_(S) to end time T_(E)) due to lots of traffic on the small cell, while there is only a small amount of traffic on the macro cell. However, the UE still needs to monitor the macro cell for a long time, resulting in extra consumption of UE power unnecessarily.

In general, as there is very little traffic via the macro cell, it should be sufficient for the UE to monitor the macro cell for radio resource allocations on the macro cell if the onDurationTimer is running. Thus, a simple solution to reduce UE power consumption would be for the UE not to monitor the macro cell if the drx-InactivityTimer is running.

Furthermore, if inter-eNB CA is applied, the macro cell and the small cell could be controlled by separate eNBs (such as a SeNB and a DeNB). In this situation, the drx-InactivityTimer could be maintained in the DeNB; and thus the UE would only need to restart this timer when receiving a PDCCH indicating a new transmission on the small cell.

Another alternative is for the UE to maintain separate drx-InactivityTimers for both cells. In this alternative, the UE would monitor a cell if its corresponding drx-InactivityTimer is running. This alternative is more flexible for inter-eNB CA because the active time of the macro cell could be extended beyond the On_Duration as needed.

Regarding the onDurationTimer, it should be more power efficient for the UE to maintain the same onDurationTimer for the macro cell and the small cell because the UE could wake up at the same time to monitor both cells.

FIG. 6 is a flow chart 600 in accordance with one exemplary embodiment. In step 605, the UE is configured with DRX and is served by a first cell that is configured with a PDCCH. In step 610, the UE receives an RRC (Radio Resource Control) message for configuring a second cell to the UE, wherein the second cell is also configured with a PDCCH. In step 615, the UE maintains separate drx-InactivityTimers for the first cell and the second cell.

In one embodiment, the first cell and the second are controlled by separate evolved Node Bs (eNBs). Furthermore, the RRC message includes information for the UE to determine whether to maintain separate drx-InactivityTimers for the first cell and the second cell. In addition, the UE would monitor the PDCCH on the first cell if the drx-InactivityTimer corresponding to the first cell is running. Similarly, the UE would monitor the PDCCH on the second cell if the drx-InactivityTimer corresponding to the second cell is running. Also, the UE would restart the drx-InactivityTimer corresponding to the first cell when the UE receives a PDCCH indicating a new transmission on the first cell. Similarly, the UE would restart the drx-InactivityTimer corresponding to the second cell when the UE receives a PDCCH indicating a new transmission on the second cell. In addition, the drx-InactivityTimer specifies a number of consecutive PDCCH-subframe(s) after successfully decoding a PDCCH indicating an initial uplink (UL) or downlink (DL) user data transmission for the UE.

In another embodiment, the UE maintains one onDurationTimer for the first cell and the second cell, wherein the onDurationTimer specifies the number of consecutive PDCCH-subframe(s) at a beginning of a DRX Cycle. Furthermore, the UE would monitor PDCCHs on the first cell and the second cell if the onDurationTimer is running.

Referring back to FIGS. 3 and 4, in one embodiment, the device 300 implements a UE that is configured with DRX and is served by a first cell that is configured with a PDCCH (Physical Downlink Control Channel). In one embodiment, the device includes a program code 312 stored in memory 310. In one embodiment, the CPU 308 could execute the program code 312 (i) to receive an RRC message for configuring a second cell to the UE, wherein the second cell is configured with a PDCCH, and (ii) to maintain separate drx-InactivityTimers, at the UE, for the first cell and the second cell. In addition, the CPU 308 can execute the program code 312 to perform all of the above-described actions and steps or others described herein.

FIG. 7 is a flow chart 700 in accordance with one exemplary embodiment. In step 705, the UE is configured with DRX and is served by a first cell that is configured with a PDCCH. In step 710, the UE receives an RRC (Radio Resource Control) message for configuring a second cell to the UE, wherein the second cell is also configured with a PDCCH. In step 715, the UE would maintain separate drx-InactivityTimers for the first cell and the second cell if both cells are controlled by the separate evolved Node Bs (eNBs). However, if both the first cell and the second cell are controlled by the same eNB, the UE would maintain one drx-InactivityTimer. In addition, the drx-InactivityTimer specifies a number of consecutive PDCCH-subframe(s) after successfully decoding a PDCCH indicating an initial uplink (UL) or downlink (DL) user data transmission for the UE.

In one embodiment, the UE maintains one onDurationTimer for the first cell and the second cell. In this embodiment, the onDurationTimer specifies the number of consecutive PDCCH-subframe(s) at a beginning of a DRX Cycle. Furthermore, the UE would monitor PDCCHs on the first cell and the second cell if the onDurationTimer is running.

Referring back to FIGS. 3 and 4, in one embodiment, the device 300 implements a UE that is configured with DRX and is served by a first cell that is configured with a PDCCH (Physical Downlink Control Channel). In one embodiment, the device includes a program code 312 stored in memory 310. In one embodiment, the CPU 308 could execute the program code 312 (i) to receive an RRC message for configuring a second cell to the UE, wherein the second cell is configured with a PDCCH, and (ii) to maintain separate drx-InactivityTimers, at the UE, for the first cell and the second cell if both cells are controlled by separate eNBs, and to maintain one drx-InactivityTimer, at the UE, for the first cell and the second cell if both cells are controlled by the same eNB. In addition, the CPU 308 can execute the program code 312 to perform all of the above-described actions and steps or others described herein.

Various aspects of the disclosure have been described above. It should be apparent that the teachings herein may be embodied in a wide variety of forms and that any specific structure, function, or both being disclosed herein is merely representative. Based on the teachings herein one skilled in the art should appreciate that an aspect disclosed herein may be implemented independently of any other aspects and that two or more of these aspects may be combined in various ways. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, such an apparatus may be implemented or such a method may be practiced using other structure, functionality, or structure and functionality in addition to or other than one or more of the aspects set forth herein. As an example of some of the above concepts, in some aspects concurrent channels may be established based on pulse repetition frequencies. In some aspects concurrent channels may be established based on pulse position or offsets. In some aspects concurrent channels may be established based on time hopping sequences. In some aspects concurrent channels may be established based on pulse repetition frequencies, pulse positions or offsets, and time hopping sequences.

Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

Those of skill would further appreciate that the various illustrative logical blocks, modules, processors, means, circuits, and algorithm steps described in connection with the aspects disclosed herein may be implemented as electronic hardware (e.g., a digital implementation, an analog implementation, or a combination of the two, which may be designed using source coding or some other technique), various forms of program or design code incorporating instructions (which may be referred to herein, for convenience, as “software” or a “software module”), or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

In addition, the various illustrative logical blocks, modules, and circuits described in connection with the aspects disclosed herein may be implemented within or performed by an integrated circuit (“IC”), an access terminal, or an access point. The IC may comprise a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, electrical components, optical components, mechanical components, or any combination thereof designed to perform the functions described herein, and may execute codes or instructions that reside within the IC, outside of the IC, or both. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

It is understood that any specific order or hierarchy of steps in any disclosed process is an example of a sample approach. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged while remaining within the scope of the present disclosure. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented.

The steps of a method or algorithm described in connection with the aspects disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module (e.g., including executable instructions and related data) and other data may reside in a data memory such as RAM memory, flash memory, ROM memory, EPROM memory. EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of computer-readable storage medium known in the art. A sample storage medium may be coupled to a machine such as, for example, a computer/processor (which may be referred to herein, for convenience, as a “processor”) such the processor can read information (e.g., code) from and write information to the storage medium. A sample storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in user equipment. In the alternative, the processor and the storage medium may reside as discrete components in user equipment. Moreover, in some aspects any suitable computer-program product may comprise a computer-readable medium comprising codes relating to one or more of the aspects of the disclosure. In some aspects a computer program product may comprise packaging materials.

While the invention has been described in connection with various aspects, it will be understood that the invention is capable of further modifications. This application is intended to cover any variations, uses or adaptation of the invention following, in general, the principles of the invention, and including such departures from the present disclosure as come within the known and customary practice within the art to which the invention pertains. 

What is claimed is:
 1. A method for discontinuous reception (DRX), wherein a UE (User Equipment) is configured with DRX and is served by a first cell that is configured with a PDCCH (Physical Downlink Control Channel), comprising: the UE receives an RRC (Radio Resource Control) message for configuring a second cell to the UE, wherein the second cell is configured with a PDCCH; and the UE maintains separate drx-InactivityTimers for the first cell and the second cell.
 2. The method of claim 1, wherein the RRC message includes information for the UE to determine whether to maintain separate drx-InactivityTimers for the first cell and the second cell.
 3. The method of claim 1, wherein the UE monitors the PDCCH on the first cell if a drx-InactivityTimer corresponding to the first cell is running and the UE monitors the PDCCH on the second cell if a drx-InactivityTimer corresponding to the second cell is running.
 4. The method of claim 1, wherein the UE restarts the drx-InactivityTimer corresponding to the first cell when receiving a PDCCH indicating a new transmission on the first cell, and restarts the drx-InactivityTimer corresponding to the second cell when receiving a PDCCH indicating a new transmission on the second cell.
 5. The method of claim 1, wherein the first cell and the second cell are controlled by separate evolved Node Bs (eNBs).
 6. The method of claim 1, wherein the UE maintains one onDurationTimer for the first cell and the second cell.
 7. The method of claim 6, wherein the onDurationTimer specifies a number of consecutive PDCCH-subframe(s) at a beginning of a DRX Cycle.
 8. The method of claim 6, wherein the UE the LIE monitors PDCCHs on the first cell and the second cell if the onDurationTimer is running.
 9. The method of claim 1, wherein the drx-InactivityTimer specifies a number of consecutive PDCCH-subframe(s) after successfully decoding a PDCCH indicating an initial uplink (UL) or downlink (DL) user data transmission for the UE.
 10. A UE (User Equipment) for discontinuous reception (DRX) in a wireless communication system, wherein the UE is configured with DRX and is served by a first cell that is configured with a PDCCH (Physical Downlink Control Channel), the UE comprising: a control circuit for realizing functions of the communications device; a central processing unit coupled to the control circuit for executing a program code to operate the control circuit; and a memory coupled to the central processing unit for storing the program code; wherein the program code comprises: receiving an RRC (Radio Resource Control) message for configuring a second cell to the UE, wherein the second cell is configured with a PDCCH; and maintaining separate drx-InactivityTimers, at the UE, for the first cell and the second cell.
 11. The UE of claim 10, wherein the RRC message includes information for the UE to determine whether to maintain separate drx-InactivityTimers for the first cell and the second cell.
 12. The UE of claim 10, wherein the UE monitors the PDCCH on the first cell if a drx-InactivityTimer corresponding to the first cell is running and the UE monitors the PDCCH on the second cell if a drx-InactivityTimer corresponding to the second cell is running.
 13. The UE of claim 10, wherein the UE restarts the drx-InactivityTimer corresponding to the first cell when receiving a PDCCH indicating a new transmission on the first cell, and restarts the drx-Inactivity Timer corresponding to the second cell when receiving a PDCCH indicating a new transmission on the second cell.
 14. The UE of claim 10, wherein the first cell and the second cell are controlled by separate evolved Node Bs (eNBs).
 15. A method for discontinuous reception (DRX), wherein a UE (User Equipment) is configured with DRX and is served by a first cell that is configured with a PDCCH (Physical Downlink Control Channel), comprising: the UE receives an RRC (Radio Resource Control) message for configuring a second cell to the UE, wherein the second cell is configured with a PDCCH; and the UE maintains separate drx-InactivityTimers for the first cell and the second cell if both cells are controlled by separate evolved Node Bs (eNBs), and the UE maintains one drx-InactivityTimer for the first cell and the second cell if both cells are controlled by one eNB.
 16. The method of claim 15, wherein the UE maintains one onDurationTimer for the first cell and the second cell.
 17. The method of claim 16, wherein the onDurationTimer specifies the number of consecutive PDCCH-subframe(s) at a beginning of a DRX Cycle.
 18. The method of claim 16, wherein the UE monitors PDCCHs on the first cell and the second cell if the onDurationTimer is running.
 19. The method of claim 15, wherein the drx-InactivityTimer specifies a number of consecutive PDCCH-subframe(s) after successfully decoding a PDCCH indicating an initial uplink (UL) or downlink (DL) user data transmission for the UE. 